Anatomic study for pubic medullary screw insertion.

PURPOSE To study the anatomy of the pubic ramus and adjacent structures in 160 Japanese to establish a safer pubic screw fixation technique. METHODS 80 male and 80 female Japanese aged 16 to 89 (mean, 50) years (10 persons in each decade of age) underwent 3-dimensional computed tomographic scanning of their pelvises. The angle at which the screw should be targeted, the appropriate length of the screw, the size of the canal for screw insertion, and the proximity to the bladder, iliac artery, and iliac vein were determined. Correlations between the canal diameters (of the acetabular, base, and parasymphyseal areas) and body features (age, height, and weight) were analysed. RESULTS In men and women respectively, the appropriate mean screw length was 124.6 and 123.8 mm; the guide wire should be targeted at a mean of 66 degrees and 67 degrees cephalad and 54.1 degrees and 55.9 degrees laterally for insertion of a retrograde pubic screw; the minimum distances from the pubis to the bladder/iliac artery/ iliac vein were 0 and 0 mm/4.9 and 4.6 mm/0.8 and 0.2 mm. In both men and women, the canal diameters at the base were positively correlated to weight. In women, the canal diameters at the parasymphyseal area were correlated to height and weight. Canal diameters at the acetabulum were not correlated to height and weight. CONCLUSION Pubic screw fixation may be potentially disastrous (owing to joint penetration and iliac vein injury) and should be performed with caution. When the canal diameter at the acetabulum is extremely narrow, plate fixation, computer-assisted surgery, or changing to a smaller-diameter screw is recommended.